Students of engine design will be familiar with a standard Wankel rotary engine. In this type of engine, the rotor with its internal ring gear is driven eccentrically about a fixed pinion. The rotor has a “constant-width” geometry: it always appears to be the same width when viewed from any angle. The particular constant-width shape used in production rotary engines is based on a Reuleaux triangle, named for the French mathematician that formally described it.
The rotor revolves with a housing of epitrochoidal geometry, so that regions of gas in the engine housing may undergo compression and ignition as a result of the rotor motion.